Efficacy of Long-Acting Formulations of Estradiol or Progesterone Plus Estradiol on Estrous Synchronization in Broodmares Academic Article uri icon


  • A preliminary trial was performed to evaluate the ability of sustained release preparations of estradiol-17 or progesterone plus estradiol-17 to synchronize estrus in cyclic mares. Group 1 mares were treated with a 50 mg intramuscular (IM) injection of sustained release estradiol-17, while group 2 mares were treated with estradiol plus 1.5 g of sustained release progesterone. All mares received an IM injection of 10 mg of prostaglandin-F2 (PGF2) 10 days after steroid treatment. Mares were examined by transrectal ultrasonography on Days 1 and 10 of treatment and then at 2 day intervals to monitor follicle size. Once a follicle 30 mm diameter and uterine edema were detected, 0.5 mg of the GnRH analog histrelin was administered IM. Mares were examined daily thereafter to detect ovulation. Group 1 mares did not exhibit ovulation synchrony (ovulations occurred 12-22 days after steroid treatment), whereas ovulation synchrony was satisfactory in group 2 mares (interval to ovulation being 20.41.5 days, range 17-22 days). Using sustained release preparations of progesterone plus estradiol-17, with PGF2 administered on Day 10, could eliminate the need for daily injections of steroid preparations in oil when synchronizing estrus and ovulation. 2013 Elsevier Inc.

published proceedings

  • Journal of Equine Veterinary Science

author list (cited authors)

  • Sudderth, A. K., Kiser, A. M., Brinsko, S. P., Love, C. C., Varner, D. D., Burns, P. J., & Blanchard, T. L.

complete list of authors

  • Sudderth, A Kendrick||Kiser, Allison M||Brinsko, Steven P||Love, Charles C||Varner, Dickson D||Burns, Patrick J||Blanchard, Terry L

publication date

  • January 1, 2013 11:11 AM